1. Field of the Invention
This invention relates to a flexible chain conveyor for a mining machine and apparatus for controlling the tension on the conveyor and more particularly to a take-up cylinder that is hydraulically operated and responsive to the operating pressure of the conveyor drive motor so that only that force required to maintain the conveyor chain free of slack is applied thereto.
2. Description of the Prior Art
In transferring dislodged material rearwardly on a mining machine by a longitudinal conveyor, it is the conventional practice to provide a conveyor discharging end portion that is pivotally connected to the main conveyor and operable to swing laterally in controlling the discharge of material from the conveyor. U.S. Pat. No. 3,190,697 discloses such a laterally swingable conveyor on a continuous mining machine. There, cutting elements of the mining machine dislodge the solid material from the mine face and a flexible, continuous flight conveyor extending rearwardly of the cutting elements transports the dislodged material to a discharging end portion of the conveyor. The discharging end portion of the conveyor includes a boom member that is connected to the machine body portion. The boom member is operable by a piston cylinder assembly to swing laterally relative to the main conveyor so that the end conveyor may be maintained in material receiving relation with a conventional haulage vehicle as the mining machine is maneuvered through the mine.
A problem, however, is encountered in maintaining a preselected tension on the conveyor chain as it swivels laterally to take-up the slack in the conveyor. To overcome the problem of slack in the conveyor chain, take-up devices such as springs, which are rigidly secured to the conveyor support frame at one end and at the opposite end to the shaft of the rear sprocket of the conveyor, maintain the conveyor under tension when it is swung laterally to prevent slack developing in the conveyor. However, a spring by maintaining tension on the conveyor when swung laterally subsequently exerts an excessive amount of tension on the conveyor discharging end portion when it is aligned with the main portion of the conveyor. The tension exerted by the spring take-up is substantially more than is necessary to maintain the conveyor free of slack when the conveyor portions are aligned. Consequently, the increased tension on the components of the chain such as the chain links, load pan, return pan, drives and bearings accelerates the wear of these components requiring increased maintenance. Furthermore, the excessive tension exerted on the conveyor chain contributes to create undesirable chain noise.
The conveyor take-up spring is connected to the rear sprocket which is longitudinally movable in the conveyor support frame. It has been the practice to drive the conveyor from the front sprocket in which the drive is located in the gathering head. This drive arrangement, because of the size of the drive sprocket, limits the location of the forward end of the conveyor chain to a point further from the leading edge of the gathering head that is desirable for an efficient gathering operation. With a front drive arrangement, the entire conveyor chain from the drive sprocket to the rear idler sprocket or roller assembly and back through the lower conveyor run to the front sprocket is under full load tension. Therefore, the chain is fully loaded when flexed or swung laterally. Slack which develops in the chain is collected immediately behind the drive sprocket. The concentration of slackened chain results in skipping of the chain if allowed to run with such an accumulation of slack. Therefore, it is desirable to drive the conveyor from the rear sprocket so that only the upper run is tensioned, and the wear and noise level is substantially reduced. By driving the conveyor from the rear sprocket and positioning an idler roller assembly at the front of the conveyor, the conveyor may be positioned closer to the gathering device to carry out a more efficient gathering operation. However, by the nature of spring take-up devices to maintain the prescribed minimum tension on the conveyor when it is swung, necessitates that an excessive amount of tension be applied to the conveyor thorugh the driven rear sprocket when the conveyor portions are aligned. It has been suggested to position spring take-up devices on the front roller assembly particularly for boring type continuous miners, but the limited area for such devices at the front of the conveyor in view of the problem of positioning the gathering device as close as possible to the front of the conveyor prevents such an arrangement.
There is need to provide a conveyor for a continuous mining machine in which a preselected tension is maintained on the conveyor to prevent slack from developing in the conveyor when it is swung laterally. The tension on the elements of the conveyor when the conveyor portions are aligned must not exceed the tension required to maintain the conveyor free of slack when swung in order to avoid excessive wear of the conveyor components and generation of unacceptable levels of noise when the conveyor is operating. Furthermore, there is need for a continuous mining machine conveyor that is driven from the rear sprocket to facilitate positioning the front sprocket relative to the gathering device for an efficient gathering operation.